Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 12,567	$ 10,693
Property, plant and equipment, less allowance for depreciation	$ 958,215	$ 902,917
Preferred stock, par value (usd per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (usd per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	450,000,000	450,000,000
Common stock, shares issued (in shares)	148,913,877	150,081,474
Common stock, shares outstanding (in shares)	148,913,877	150,081,474